1. Field of the Invention
The present invention relates to a stencil printing machine that feeds a printing medium while pressing it to a drum having a stencil sheet and transfers ink permeating through perforations in the stencil sheet to the printing medium.
2. Description of Related Art
In this kind of stencil printing machine, an applicant of this specification has proposed a stencil printing machine disclosed in Japanese Patent Laid-Open Publication No. 2005-74734. This stencil printing machine comprises a rotary drum having an outer circumferential wall formed by an ink impermeable member, a stencil clamping part for clamping a leading end of stencil sheet, ink supply unit having an ink supply opening formed on the outer circumferential wall to supply a surface of the outer circumferential wall with ink, a press roll adapted so as to be movable between a press position for pressing the outer circumferential wall and a standby position apart from the outer circumferential wall, for pressing the stencil sheet against the outer circumferential wall, and ink recovery means (unit) having an ink recovery opening formed on a “printing” downstream side of a maximum printing area defined on the outer circumferential wall to collect “runoff” ink into the ink recovery opening by suction.
In printing, the outer circumferential wall equipped with the stencil sheet is rotated. When supplying a printing paper on condition that the outer circumferential wall is supplied with ink through the ink supply opening, the printing paper is transported while being pressed on the stencil sheet and the outer circumferential wall of the drum by the press roll. Meanwhile, the ink between the outer circumferential wall and the stencil sheet is diffused toward the “printing” downstream side in the printing direction by the pressure of the press roll. Simultaneously, the diffused ink exuding out through perforations in the stencil sheet is transferred on the printing paper, so that an ink image is printed on the paper. Note that, the ink on supply is retained in a substantially closed space between the outer circumferential wall and the stencil sheet, keeping ink's contact with atmosphere to a minimum. Additionally, there is no need of arranging a variety of rolls for ink supply in the drum. Thus, the above-mentioned printing machine has an advantage that the ink would not degenerate in spite of a long interval between the printing operations. Further, it is possible to miniaturize and lighten the drum itself.
Meanwhile, a stencil fitting operation to fit the stencil sheet to the outer circumferential wall of the drum is accomplished by the following steps of: clamping the leading end of the stencil sheet by the stencil clamping part; gradually winding the stencil sheet around the outer circumferential wall while rotating the drum; cutting the stencil sheet by a predetermined length during the above winding; and further rotating the outer circumferential wall after cutting the stencil sheet thereby winding the so-cut stencil sheet of the predetermined length around the outer circumferential wall of the drum.
In the conventional stencil printing machine mentioned above, however, the ink rarely remains on the surface of the outer circumferential wall once the stencil sheet is discharged from the outer circumferential wall because it is formed by the ink impermeable member. Even if it remains, the residual ink would be dried immediately. Thus, since the above stencil fitting operation is performed under condition of establishing no ink-viscosity on the outer circumferential wall, it is impossible to wind the stencil sheet around the drum with no wrinkle by the following reason.
That is, if the ink-viscosity exists on the outer circumferential wall, the stencil sheet wound around the outer circumferential wall with no wrinkle could maintain its winding state owing to the ink-viscosity. Therefore, even when tension is removed away from the stencil sheet by its reaction force at cutting, there is no possibility that the stencil sheet wrinkles up. However, in case of the outer circumferential wall formed by the ink impermeable member, the stencil sheet wrinkles up with ease due to the reaction force at cutting or the application of no tension after cutting. It follows that it is impossible to wind the stencil sheet around the drum without producing any wrinkle.